Telephone system utilizing a register controller



Nov. 2, 1948. J. KRUITHoF ETAL 452578 TELEPHONE SYSTEM UTILIZING A REGISTER CONTROLLER 5 Sheets-Sheet l Filed Jan. 22, 1945 IIL 1 Nov., 2, 1948.

J. KRUITHOF ETAL Filed Jan. 22, .1943

TELEPHONE SYSTEM UTILIZING A REGISTER CONTROLLER- 5 Sheets-Sheet 2 Nog'. 2, 19548. J. KRUITHoF ETAL TELEPHONE SYSTEM UTILIZING A REGISTER CONTROLLER Filed Jan. 22, 1943 5 sheets-sheet s INVENTORS NGV 2 194'@- J. KRUITHOF ET AL 2,452,578

TELEPHONE SYSTEM UTILIZING A -REGISTER CONTROLLER Filed Jan. 22, 194s 5 sheets-sheet 4 Nov. 2, 1948. -J. Kreun-HOF ErAL 2,452,578

TELEPHONE- SYSTEM UTILIZING 'A REGISTER CONTROLLER Filed Jan. 22, 1943 5 Sheets-Sheet 5 ATTORNEY Patented Nov. 2, 1948 TELEPHNE SYSTEM UTILIZING A REGISTER CONTRLLER Jacob Kruithof, Ladislas Kozma, and Martinus den Hertog, Antwerp, Belgium, assignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application January 22, 1943, Serial No. 473,278 In the Netherlands May 20, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires May 20, 1961 16 Claims.

The invention relates to automatic or semiautomatic telephone and similar systems, in which one or more group selector stages are used.

In telephone or similar systems (so-called telecommunication systems) automatic switching systems or stages are employed comprising group selectors and iina1 selectors, which are operable to select a free outlet in a predetermined group, or (in a final selector) a particular predetermined outlet.

This invention deals particularly with methods of operating stages of group selectors in such systems. Two distinct functions are performed in a group selecting stage, viz. the selection of a particular group of outlets, and the hunting for a free outlet in the selected group of of outlets. The selecting action is controlled either directly or indirectly by the calling subscriber, who must in some way or another indicate the destination of the connection. The hunting action takes place automatically, independently of the calling subscriber, and is performed by the automatic group selector stage or equipment itself.

Group selectors of different types may be divided into forward or directive impulse types which have a step-by-step movement, and revertive impulse types in which driving power is obtained from a common motor.

Group selectors are known in which power may be applied either from a common motor or from a source individual to the selector and which are not controlled by directive or revertive but by marking impulses. In such systems forward or revertive impulses are used to set a separate marker switch, which may be either individual to a selector or common to a plurality of selectors, and which connects a, marking potential to the so-called marking level of the selector bank.

Step-by-step switches are usually provided with a selector bank of ten levels, each containing a certain number of sets of bank contacts, each serving an individual outlet. The selecting movement in this case is used to bring the wipers of the brush carriage to a particular level, and the hunting movement is made by letting these wipers pass over the diiierent sets of bank contacts of the selected level. The number of accessible outlets is limited to the number available in each level. This number is invariable, because it is determined by the construction of the switch.

The revertive impulse type of selector switch is usually controlled by a register controller and has bank contacts containing a larger number of ou"- lets in each level than the directively controlled switch, because the register controller allows for hunting over a period independent of the speed of sending the numerical indications denoting the destination of the connection. In principle, however, the arrangement of the selector bank has the above mentioned limitations because the number of outlets in each level is limited by the construction of the switch. This may in a good many cases lead to an uneconomical employment of the selector switch.

The marker type of switch has usually a single motion and its bank contacts are arranged in one row which is wiped over by a single set of brushes. The bank contacts may be arranged in two rows, which are wiped over by two sets of brushes staggered Other arrangements are also known which insure that all sets of contacts in the bank will be reached during one cyclic operation of the brush carriage.

In such switches the sets of bank contacts are subdivided into any number of groups, as dictated by the switching requirements, and each group may contain any number of outlets. only limitation is that the sum of the outlets for each group do not exceed the total number of sets of bank contacts provided in the bank.

One disadvantage of all single motion switches is that it cannot be used alone, but must always have some helping mechanism, viz. a marker switch. This circumstance more or less outweighs the advantage of the single motion switch over the two-motion switch. Moreover, marker systems require, in some cases, the provision of complicated common control circuits. In the absence of a common control circuit one marker switch per selector would have to be provided. Since the marker switch is used only during the setting of the selector onto a free outlet in the wanted group, it is not used most of the time when provided individually per selector. On the other hand, if a control circuit is provided, then upon its use for one of the selectors all other selectors become temporarily disabled and must wait for the control circuit to become free. Furthermore, the common control circuit constitutes a vulnerable point in the switching system and damage to it endangers the whole system.

The present invention relates to a switching system using single motion switches requiring no control circuits and no marker switches. The selecting and hunting operations are controlled by a common register controller which serves all of the switching stages without the interposition of any marking system or similar expedients.

Whenever in prior systems single motion The svvitches were employed Without markers, either associated with the selector or in a common com trol circuit, marking connections were Aprovided to the marking level .of the selector directly yfrom a register controller. Such systems have been employed only on a limited scale and in a limited number of selector stages, because the marking multiple must be either common to all register controllers, in which case only one selection can be made at a time infeach selectingstage, or it must be divided into a :number of splits which are connected by means oi some connecting arrangement to a particular register-controller, but only when required, .in which case .these connecting arrangements are the source oi considerable complication and confusion, besides being expensive.

In the system embodying the various lfeatures of the present invention there is no limitation as to the number of connections that may be handled simultaneously, and .there are no such complications as the provision of a connection from the marking level to the register controller handling the connection. I

One possible method of eiecting direct control of selecting and hunting from common register controllers is to do this by means of revertive impulsingy i. e. by sending a make impulse or a break impulse in a closed circuit from a moving selector to the register controller, either when each group of outlets .is reached or when each individual bank contact is engaged .by the wipers of the selector.

When considering the sending of an impulse for every group, it should be borne in mind that the manner in which the groups can be divided in the bank is rather restricted. This is so icecause it is desirable to keep this division as simple as possible, and thus not to complicate the arrangement at the register controller where a switch must be provided having Wipers advancing one step for each revertive .impulse received from the selector under control for thepurpose of permitting the selector to `test only one group of outlets in a particular predetermined position.

If the outlets of one level were divided at random over the Whole bank, the switch at the register controller would have many positions in which it'permits the selector to test, and still many more positions in which it does not permit the selector to test. A revertive impulse would have to be sent each time the selector wipers reach outlets belonging to a .diierent group. Changes in the arrangement of the group selector outlets would then be reflected in a changed arrangement at the registercontrollers, etc. A

The sending of a revertive Yimpulse for each bank contact passed over by a selector Wiper is one Way of doing this, though in an extreme case the switch at the register may have vto be provided with as many positions as there are sets oi bank contacts in the selector.

VBoth arrangements have the lgeneral disadvantage that they require at the controller a moving switch capable of following fast and accurately the .impulses received from the selector.

According to the `present invention single motion switches are directly controlled from register controllers Without using revertive impulses and without the necessity of providing movable apparatus at the register controller.

We employ the signaling `system described in the co-pending application Serial No. l'72,b23J 'Filed January 16, 1943, by Simon et al., now Patent No. 2,424,585, dated July 29, 1947, in which 4 use is made of a plurality oi sources of current to differentiate between the dierent groups of outlets inthe 4selector bank.

When the selector brushes .move over `the bank contacts of a particular outlet, a signal is transmitted from the selector to the register controller for each outlet passed over by the brushes. This signal is characteristic for the particular group and will inform the register of the fact that the selector engages a set of bank contacts of the group of outlets to be selected.

No distinct selecting and hunting operations are performed and the selector moves under the control of the register controller until its wipers iind an outlet having on its test terminal the particular signaling current to which the register controller is set to respond. One of the advantages of this scheme is that the selector circuit is extremely simple, only two relays being required to control the single motion selector which itself is of very simple design, since it performs only a single movement. Furthermore, the speed of operation may be extremely high. The absence of directive or `revertive impulses is also an advantage as is the absence of mechanism for counting these impulses at the selector or in association with the selector and at the register controller. Moreovery the arrangement of the outlets in the selector bank is flexible, because the outlets may be arranged in any conceivable manner, Without requiring a corresponding adaptation at the register controller. Due to the absence of a marking multiple, the num-ber of simultaneous selections is not limited, and no such artificial load is placed on the selectors as is the case when a common control circuit is taken into use for one of the selectors of the group served. The system has no such vulnerable part as a common control circuit. The Wiring of the selector banks is extremely simple, because there are no marking levels which have to be split according to the size of the group to be served by one control circuit or to be served by one set of connecting apparatus establishing a connection with the register controllers.

Description of the circuit operation The invention will now be described with the aid of the drawings in which so much of a telephone exchange asis necessary to understand the invention is diagrammatically illustrated. Figs. l, 2 and 3 should be placedone 'below the other. They represent a 'register controller, but illustrate only those parts thereof Which are required for the understanding of the selecting operation. Fig. 4 illustrates a group selector and should be placed to the right of Fig. 1. Fig. 5 is an alternative. for Fig. 4.

It is assumed that a subscribers call is picked up by line .nders in the known Way and that a register circuit is attached to the calling line over a suitable linkcircuit. The group selectors of the different stages have all the same circuit as shown in Fig. 4, with the exception of a slight modification in the Wiring, so that the wires marked may be left out in the first group selector. It is assumed that the first group selector is permanently connected to the customary second line inder circuit and is, therefore, engaged without preceding selection. The second and third group selectors are identical. Figs. l, 2 and 3 control three selections, viz. those performed .by the iirst, second and third group selectors, whereupon the final selector is reached.

(a) Reception-of digits i gizes there'lays Lbr and Lhr. Relay vLbr is aslowl releasing relay andremains operated during dial impulsing. I

`Tli`e first digit is stored on the step-by-step switch SM1. On the first opening of the "dial-con-v tacts magnet SM1 is "energized over the'mcircuit': ground, Isrback, Lbr front, winding Lmr,"Dir1 back, magnet SM1, battery.

Relay Lmr operates onvthe first impulse and remains" energized during the train o'fimpulses 'of one digit. Switch SM1 advances by one step each time relay Isr releases and stops nally in a position.,corresponding to the number` sent by the subscriber.

Y rRelay'Isr remains during the interdig-ital time on its front for a time suicient to release relay Lmr. The switch magnet'IM was kept operated by relay Lmr during the reception of the digit, becomes deenergized and moves its brushes (Fig. 2)- into position whereupon relay Dzr1 operates.

Relay Dz'r1 changes overl the stepping circuit from` switch SM1 to SM2 over a front contact of Dz'ri and a back contact of Dirz so that the second digit will be received by switch` SM2 in the same way as the first digit was received by SM1. lThe magnet of switch IM is againkept energized during the reception of the dial impulses upon the termination of which relay Dirz operates.l The third digit will be directed to switch SMS. Upon the reception of the third digit relay Dirs is energized. The reception of further digits is not shown in the drawing.

Relay Chr (Fig. 2) is controlled at the front of relay Iszr and it therefore follows the impulses of the rst digit. The circuit extends;` ground Isr front, Ftr back, Vtr back, Chr, battery. The purpose of this relay will appear from the description below.

(b) Alternating current testingL las soon as the first impulse of the rst digit has been registered by switch SM1, the first group selector switch starts to rotate in hunt for a free second group selector in thefgroup indicatedloy.l switch SM1. For the sake of simplicity we'willv first consider one hundred point selector switches with ten groups of outlets, each group having ten such outlets. Y The selector switch has its normal position in front of the group corresponding to they number 0. The next group, corresponding to the number l starts ten terminals further, the group for number 2 again ten terminals further, etc. Assuming that the dial impulses are received faster than the advance of the brushes of the selector switch over the different groups, when the brushes of switch SM1 (shown below the magnet in Fig. 3) come to rest on the terminal corresponding to the digit sent, the brushes of the selector will not yet have reached the first outlet of the coresponding group. It willbe explained'later under the heading Speedup that the circuit operationis correctunder all switching conditions with different time limit.

As soon as the register is engaged, relay Ar (Fig. 4) loperates over the circuit: ground, brush and normalterminal a of switch SM1,` Lhrfront, y

bf wire, Br back, Ar back, Ar,l battery. Ar locks itself l'over the d wirelto 1the -front of Lhr.

The power magnetl P of the A'selector switch' brush c of switch OM, Vbiback, Ftr back'i/'rrv back, al wire, Br back; Ar front', magneti',`

battery. I

' The selection is determined by comparingl the alternating current signal received from the group selector with the alternating current signal available over the arcs b of switches SM1-3, These two currentsarev compared in the register con-l troller.

tubes T1, T2 and relay Vtr.

The operation of this equipment has been de scribed in full detail in the above mentioned ap` plication. yThe signaling current is the alternating .current received from the selector circuit and the reference current is the alternating currentv connected over the arcs of switches SM1-3.`

The circuit of the signaling current can be traced as follows: The source of alternating current Sresistance R1 of 100e, home contact of 'the The circuit for the reference current is asiel` lows: The alternating current source Ref. (Fig.

3) resistance of i001, terminal b of switch SM1,l to which it was set, normal terminal and brush' d of Switch OM,

transformer HCz.

When equipment detects that the signaling and and theprimary winding ofv the reference currents are in phase, then the cold' cathode tube T2 becomesionized, relay Vtr operates and consequently the selector stops on the terminals of an outlet in the wanted group.

Upon the energizing of relay Vtr, relay Ftrfi's' energized over the circuit: ground, brush a and terminal l of arcl of switch SM1, terminal N and brush c of switch OM, Vt'r front, Fhr back, winding of relay Ftr, battery.

Relayv Ftr prepares a locking circuit for itself overv the Iwinding of Fhr and opens the circuit of Chr.` Chr'removes the 130 volt positive battery from the anode of the tube T2. 'Vtr releases and removes the short-circuiting ground from relay Fhr and this relay operates in 'series with relay Ftr via back of Vrr and front of relay Lhr. Relay Fhr again closes the operating circuit of relay Chr, which operates sothat the tube T2 lights again, thealternatingcurrent signal from the selector being still sent. Relay Vtr operates again and closes the following circuit :for'relay Str: ground on the armature of Vtr, Fhr front, winding of relay Str, battery. j

The operation of relay Str signifies that the alternating current test is completed and the register may proceed with the direct current test. f The alternating current test is made twice in order to make sure that the selector switch is standing on the terminals of the outlet on which it was stopped.

(c) Direct current testing The comparing equipment is shown in*` Fig. 2 Aand includes transformers HC1, HCzgVI,

anatre" 7 tor, Ar back, resistance a2 cf sooo, battery in the second group selector. y

In this circuit relay Tr alone can operate and relay Br, due to the high resistance of relay Tr, does not operate. The front of Tr connects relay Dtr and its low resistance winding in parallel to its own high resistance winding making the test potential of 60Go busy against other calls and increasing at the same time the current so that Br can operate. Relay Dtr is a marginal relay and can only operate if it alone is connectedto the test potential. Upon the energizing of relay Dtr relay Sar is energized. Relay Sar energizes the step-by-step switch OM as well as the relay Vrr.

Relay Vrr opens the locking circuit of Fhr and Ftr which release together with relay Str. The test relays, however, remain operated due to the second ground connected to the front of Tr via afront of Sar. Relay Vrr releases relay Chr so that the tube T2 becomes extinguished and relay Vtr releases.

After being energized relay Sarlocks itself to the interrupter contact of switch OM to make such that switch OM is fully energized. When the first group selector is connected-through by the -operated relay Br and the seizure relay Ar in the second group selector is energized, the 600 w test potential R2 is disconnected. This part of the circuit operation will be 'given in detail below.

In the register controller relay Dtr releases when the test potential is removed and, if switch OM at this moment is already fully energized, relay Sar releases. The brushes of switch OM now make one step and arrive at terminal I.

Relay Sarreleases relay Vrr and this in turn allows the reoperation of relay Chr, so that now the receiving equipment is ready for the next test.

The ground of the low resistance circuit oi relay Tr and relay Dtr is controlled over different contacts. VDetails of this circuit will be given under Speed-up.

(d) Group selector cor/meetelt through Relay Br in the rst group selector starts to operate as soonas the high resistance winding of relay Tr is shunted by relay Dtr. Relay Br is slightly slow-to operate due to its short-circuited second winding thus to cover the releasing time of the test relays in case of simultaneous tests by two or more circuits.

As soon as relay Br operates, it removes the short-circuit from its Winding II and provides a locking circuit to the battery over resistance R2. In addition, it short-circuits its operating winding I via a front contact which closes later than the shortecircuiting back contact.

The signaling current still available from the second group selector over brush d of the first group selector is rendered busy by a full ground connected over a front of relay Br. The left-hand side contacts of Br connect through the b and c wires in such a that the test potential of the second group selector over the brush "c is continually guarded.

When relay Str operates after successful alter nating current testing, it disconnects the primary winding of transformer HC1 and replaces it by a second low resistance winding of relay Dtr When relay Br energizes, it connects this second winding of relay Dt-r over its left outer change-over contact to the c wire in parallel with the other windingI of relay Dtr.. `Theinner change-over-contact at the left-hand side conlll nects through the b wire towards the second group selector. At this moment the test potential is guarded bythe second Winding II of relay Dtr5 At the moment the b wire is connectedlv of relay'Br in the first group selector. The alter nating current which was already short-circuited by the above mentioned ground is now disconnected at the back of relay Ar in the second group selector. Relay Ar disconnects also the direct current test potential of 600 w, whereupon relay Dtr becomes cle-energized as above described.

(e) Failure of the alternating current test The alternating current test is repeated in order to make sure that the group selector after stopping engages the terminal d of the group selector of the next stage. Should it happen that the brushes of the selector move too far so that the circuit over brush d is opened, then the following changes take place:

On the rst operation of relay Vtr, relays Ftr and Fhr also operate as above described. Relay Chr connects the positive battery to the tube Tr.. but the tube does not operate and relay Vtr remains deenergized. Relay Kir energizes in the circuit: ground on the armature of relay Vtr. Vtr back, Ftr front, Fhr front, relay Kir, battery.

Relay Kir energizes relay Vrr, which releases relays Ftr and Fhr. Relay Kir releases as soon as relay Fhr opens its front contacts so that Vrr upon releasing re-establishes the alternating current test conditions as before. The power magnet of the group selector is energized again and the brush carriage continues to hunt for another free outlet in the wanted group.

(j) Failure of direct current test The direct current test may fail if the stopping of the selector switch is delayed, so that the circuit over brush c is opened, or in case the test potential is kept busy by another circuit which has just performed the same alternating current test, or because the fuse of the outlet engaged is out.

In all these cases relay Tr does not operate and the relay Gbr is energized.

Relay Gbr disconnects the test relay Tr and connects the b wire tothe control cathode of the cold cathode tube T3. At the same time this relay energizes the power magnet of the selector switch over the a wire. The brush carriage leaves the position in which the direct current test was not successful and will advance until it reaches the rst free test potential of any free outlet.

The control cathode of tube T3 is permanently connected to a positive battery of about 30 v. The control anode is connected to ground. The tube therefore will not light on busied test potential, because the 30 v. is not suicient to break down the discharge space. As soon as a free potential .of 48 v. is found, the potential diiierence increases to 78 v. and the tube becomes ionized. Relay Fsr operates and stops the selector on the terminals of a free outlet which, of course, does not necessarily belong to the same group as the loutlet tested before. Relayv Fsr energizes Vrr, which causes the release of relays Fhr, Fir, Str as well as Chr and Vtr.

The release of relay Str is followed by that of relay Gbr, whereupon the tube T3 is extinguished and relay Fsr releases. The circuit is now ready to start again the alternating current test, If, therefore, the group selector does not reach the contacts of the group designated by the reference current, then the selector switches will have to start again to rotate.

(g) Speed-up The speed-up arrangement has for its purpose vto speed up the selection and it consists in that the rotation of the selector brushes takes place simultaneously with the reception of the numerical indication designating the group of outlets, a free one of which must be selected.

The first requirement is that the outlets of the switching stages be connected to the banks of the preceding selector switches in the same order as the numbering of the dial by means of which the subscriber send the digits. The second requirement is that the time required by the selector brushesv to wipe over the terminals of any of the outlets should be greater, or at least equal to the time taken by one dial impulse. It is further necessary to provide the group selector with a home position from which its brushes start their hunting operation.

The second requirement concerns the speed at which the selector brushes have to rotate. This speed will depend on the number of outlets in the different groups. Large groups can be split into several smaller groups and spread over the whole arc in any convenient way, but the section which is rst encountered by the rotating brushes of the selector must be large enough to require a rotating time at least equal to one dial impulse.

The home position of the selector brushes is fixed in such a way that normally the brush carriage is one outlet behind the position of the stepby-step switch SM. If, therefore, the` selector reaches the rst outlet of a group, the switch SM will already connect the reference current of the following group and the selector brushes will not stop. If, however, the brushes of the switch SM have been already set into the required position, the selector brushes will stop on the rst free outlet because the signaling current received through this outlet will be identical with the reference current. However, the idle outlet thus found cannot be definitely engaged until the release of the slow relay Lmr indicates with certainty that no more impulses will be sent, i. e. that the digit received is complete.

The dial speed may be variable (8-14 steps per sec.) and it may happen that in case of a very slow dial the selector reaches a free outlet in a group whilst this is still indicated by the position of switch SM. The tube T2 operates in this case and the selector brushes stop. If now a further impulse is received. then the tube T2 has'to be extinguished and the-"selector brushes have'to rotate again. It may also happen that in the case just mentioned. all outlets of the group are occupied and therefore the selector brushes cannot stop. but go over to the outlets of the next group. As a consequence of this the selector brushes may advance too far. beyond the group indicated by SM. The selection, however, will be correct under all circumstances because the selector brushes can only stop in response to the predetermined signaling current. --The selector brushes must,there l0 fore, continue their rotation until they find a free outlet in the desired group.

The above requirements are satisfied by the following circuit arrangements;

The brushes of the first group selector switch start to rotate when the brushes of switch SM1 are advanced by the first impulse to terminal l. Relay Chr follows the impulses and on each opening it removes the v. battery from the anode of tube T2. As soon as the digit is complete relay Chr remains energized, whilst relay Lmr releases and the brushes of switch IM take one step. Relay Dz'rl operates and provides a holding ground for Chr via arc a of switch OM. Relay Chr remains operated until the selection is terminated and is released by relay Vrr.

Should the brushes of the group selector, on account of low dial speed, stop on the terminal of an outlet which is not the Wanted one, then relay Chr releases when the next impulse is received and extinguishes the tube T2, releasing thereby relay Vtr and forcing the group selector to leave its position. When relay Chr re-operates, the brushes of the switch SM1 will already be in the next position and connect another reference current.

If the i'lrst selection is terminated before the second digit is sent, or whilst it is being sent,y then relay Chr follows again the impulses, acting on relay Isr, and the speedup takes place in the second group selector.

An outlet tested by alternating current can be definitely engaged only when relay Lmr is released.. When the alternating current test is completed and relay Str operates, only the high resistance winding of Tris connected towards the test potential, and no circuit will be found for the low resistance winding of relay Tr and, therefore, for relay Dtr. This circuit will be closed as soon as relay Lmr releases. On the other hand, if the digit has already been received when the alternating current test takes place, then the outlet will be immediately engaged by the complete direct current test, ground 'being provided via front of relay Dir and arc b of switch vOM independently of the back of relay Lmr, which may already be open due to the reception of the next digit.

(h) Circuit variants The above disclosed circuits and operations have been described by way of example only. It is evident that obviously, the invention is in no way limited to the specific arrangements described, and many alternatives are possible.

For example, in the circuits described the selector switches have a home position to which they are returned upon the termination of each call, a switch becoming available for the next call only when the home yposition is reached. This may be varied so that no home position is provided, in which case the home contact, certain relay contacts and wiring connections. which lare required for controlling the return to the normal position may be omitted. In this case it may be preferred to omit the speed-up feature which permits a group selector to commence moving while the numerical indication is being received at the register controller, and instead to commence the selecting and hunting action only when the numerical indication has been completely received.

The. group selector switch may be of a variety of designs. The example disclosed herein is a single-motion switch with common motor drive',

Vl l but switches with individual step-by-step movement or having individual motors or of I,any other .design may be used.

Inr the example given the characteristic potential is opened at a relay contact of the selector circuit immediately after seizure by a preceding selector. This is not essential for the operation oi the system and is suggested only in order to .permit the brush of a hunting selector switch to .pass a busy terminal Without stopping mornen- 1 .tarily. By omitting this contact` the selecting and vhunting actions would be segregated, because the brushes of the switch would in one continuous movement go to the rst outlet of a group and subsequently commence a step-by-step movement from one terminal to the next until a free outlet is found, each terminal being tested for `free .or busy condition while the switch stopped on it.

The arrangement of the two relays in the circuit .can also be varied. The circuit may, e. g., be designed so that the seizure relay is released by the operation of the switch-through relay, and the latter being made to hold onto the preceding selector, or independent of the former relay. Arb other possibility is so to design the circuit that the seizure relay is operated as long as the circuit Vis engaged for a connection, but that the second relay, denoted as the switch-through relay, is so connected that it operates during the selection and hunting action only. This leads to still another possibility, viz. to combine the functions of the power lmagnet oi the switch with that of the last-mentioned relay by placing the relevantcontact springs on the magnet assembly so that they are operated only :when the switch magnet is energized. In this Way thesecond relay coil and armature may be omitted. A circuit of this kind, which therefore has one relay only, is shown by way of yexample in Fig. In, thisiigure the brushes a, b, c, d areon terminals of .the home position. The armatures p1, p2, p3 and p4 are operated by the selector magnet.

What is claimed is:

1. Ina telecommunication system, a plurality of Anumerically designated lines, selector switches for connecting a calling line` towards a called line, said selectors having cyclically operated movable contactsv and cooperating sets of stationarv bank contacts over all of which said movable contacts move consecutively during each cycle, electromagnetic lmeans for controlling the movement of said movable contacts, groups of outlets connected in .multiple to the bank contacts of allselectors, a register controller, Vmeans for temporarily associating said register controller with a selector, means associated with the calling line for operating said-controller to register the numericaldesignation of the called line, aicontrol circuitextending from the register con.- troller to .the connected selector .for controlling said movable .contacts toselect Aa group of outlets determined .by the numerical designation oi the called line and to hunt for an idle .outlet inthe selected group, means in the connected selector forapplyinga signaling `potential to the control circuit which is characteristic for an outlet with which the movable contacts are connected, there being a plurality of diierent sources of potential,

each characteristic for a Vdiierent outlet, and a responsive device for controlling the operation or" the controller actuated by `thesignaling potential.

2. The arrangement of claim l, characterized in that each group of outlets is identified by a characteristic source ofpotential l`applied to a bank contact.

3. The arrangement oi" claim l, characterized in that each group of outlets is identified by a characteristic source of alternating current potential applied to a bank contact.

4.. The arrangement according to claim 1, characterized in that an outlet seized by the movable contacts of a selector is made busy in the bank contacts of all the other selectors, and means' for applying the characteristic signaling potential only to the bank contacts of idle outlets.

5. The arrangement according to claim l, characterized by means jointly controlled by the controller and the selector connected therewith for simultaneously performing the selecting and hunting operations thereof.

6. The arrangement of claim 1, characterized in that signal receiving equipment at the register controller is set under the control of the numerical design-ation of the called line, said arrangement further including a circuit for the electromagnetic meansof the connected selector extending to said controller, means in the controller for closing said circuit upon the beginning o the operation of the controller in accordance with the designation'of the called line, and means in the controller for opening the last mentioned circuit upon the completion of the hunting movement of the selector contacts.

7. The arrangement of Aclaim l, characterized by test means in the .register controller, a circuit for said test means closed upon thestopping of the contacts of `the connected selector switch, a source of direct current potential applied to the last mentioned circuit at the selector, and a circuit for the electromagnetic means controlled by said test means.

8. The arrangement of claim l, characterized by a switch-through relay at the selector switch, means controlled by the register controller for operating said switch-through relay upon the completion of the hunting, a cchromatin-iai condition established through said .selector upon the operation-of said relay, and means for rendering the characteristic potential of an-outlet ineffective for selecting and hunting selector switches controlled by said relay.

9. The arrangement of claim 1, characterized by Aa .switch-through relay at each selector for completing the connection through an outlet, a test relay .at the register controller, a circuit for the electromagnetic `means forsaid selectors controlled by said test relay, and a potential of direct current providedat each-outlet for operating said switch-through and test relays.

10. The yarrangement of claim 1 characterized by .a switch-through relay at each selector for completing the connection through ,an outlet, a test relay at the register controller, a circuit -ior the electromagnetic meansfor said selectors controlled by said test relay, and a potential of fdirect cnrrentprovided at eachoutlet for operating said switch-through and test relays,.and a locking circuit ior the switch-.through relay independent of the register .controller Aand .the direct current potential at the engaged outlet.

ll. In a telecommunication system, a plurality oi numerically designated lines, selector switches arranged in successive stages Vfor connecting a. calling 4'line towards .a called line, said selectors having cyclically .operated movable contacts and cooperating sets .of stationary `bank contacts over all of which said movable contacts move consecutively during each cycle, electromagnetic means for controlling Ythe movement of said mov-able contacts. groups kof .outlets .connected in .multiple to the bank contacts of all selectors of a stage, a register controller, means for temporarily associating said register controller with selectors of successive stages, a seizure relay at each selector operated upon its connection with the controller, a locking circuit for the relay independent of the controller, means associated with the calling line for operating said controller to register the numerical designation of the called line, a control circuit extending from the register controller to the connected selector for controlling its movable contacts to select a group of outlets determined by the numerical designation of the called line and to hunt for an idle outlet in the selected group, means in the connected selector for applying a signaling potential to the control circuit which is characteristic for an outlet with which the movable contacts are connected, there being a plurality of different sources of potential, each characteristic for a different outlet, a busy test potential applied to the multiples of an engaged outlet under the control of said relay, means for disconnecting the characteristic signaling potential applied at a selector of one stage controlled by the relay of the selector of the succeeding stage, and a responsive device for controlling the operation of the register controller actuated by the signaling potential.

12. In a telecommunication system, a plurality of numerically designated lines, selector switches for connecting a calling line towards a called line, said selectors having cyclically operated movable contacts and cooperating sets of stationary bank contacts over all of which said movable contacts move consecutively during each cycle, electromagnetic means for controlling the movement of said movable contacts, groups of outlets connected in multiple to the bank contacts of all selectors, a. register controller, means for temporarily associating said register controller with a selector, means associated with the calling line for operating said controllery to register the numerical designation of the called line, a control circuit extending from the register controller to the connected selector for controlling said movable contacts to select a group of outlets determined by the numerical designation of the called line and to hunt for an idle outlet in said group, means in the connected selector for applying a signaling potential to the control circuit which is characteristic of an outlet with which the movable contacts are connected, there being a plurality of different sources of potential, each characteristic for a dierent outlet, a responsive device 'for controlling the operation of the controller actuated by the signaling potential, means for applying a source of test potential to the multiples of an outlet, a test relay in the controller actuated from said source of testn potential, and an energizing circuit for the electromagnetic means controlled by said test relay.

13. The arrangement of claim l, characterized in that the movable contacts of each selector are brushes, one of which engages its cooperating bank contact later than the other brushes when moving towards a set of contacts and opens earlier than the other brushes when leaving a set of contacts, said arrangement further including test relays at the register controller operable upon the engagement by the selector brushes on the contacts of a wanted outlet, a source of test potential connected to the contact bank of a selector, and circuits for operating said test relays from said sources of characteristic potential and test potential.

14. The arrangement of claim 1, characterized in that the movable selector contacts have a normal position, and means for moving them into the normal position after the completion of a connection.

15. The arrangement of claim 1, characterized in that each selector switch is provided with two relays only for controlling all said operations.

16. The arrangement of claim 1, characterized in that the electromagnetic means of a selector is a magnet having contact springs, and a relay having conltact springs associated with each selector, all the circuits of a selector being REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date Netherlands Feb. 16. 1946 Number 

